The present invention relates to a light diffusing lens intended to be used in traffic lights of the known type, in which a generally point formed light source via a mirror, preferably a parabolic mirror, projects a nearly parallel light beam onto an un-coloured or coloured (red, yellow, green) lens adapted to scatter the light within certain predetermined limits.
Normally it is desired to scatter at least the main part of the light passing the lens over an angle downwards from the horizontal plane of about 20.degree. and over an angle aside of the vertical optical axis of about 30.degree. in other directions. On the contrary it is not desired to have the light scatter in the direction upwards.
FIG. 1 diagrammatically illustrates the international standard adopted by "CIE 1980" and which shows the desired light scattering of traffic lights. It is evident that it is desired to have a main light scattering within a substantially rectangular area restricted for instance by an angle of between +/-30.degree. from a vertical axis v-v and by an angle extending from the horizontal plane h-h and 20.degree. downwards.
Many different types of optical lenses are used for traffic lights, for instance the lenses shown in the two U.S. Pat. Nos. 2,907,249 and 3,807,834. Both said types of lenses are, at the inner surface thereof formed with light refracting elements in the form of bulges of different shape and size directed inwardly towards the light source and intended to give the desired light refraction. It may be difficult and expensive to manufacture such lenses, and normally said lenses give other light refractions than the desired light refraction according to the above mentioned adopted standards. In particular many known lenses give a poor light refraction to the two lower-outer corners at the angle 30/20 (or 20/10, 105 etc.). Other known lenses may give a too strong or a too poor light refraction either to the sides or downwards, or they may give a non-desired light refraction in the direction upwards.
Therefore, the basis of the invention is to solve the problem of providing a light diffusing lens which gives an optimum light refraction, especially a light refraction which covers an optimumly large part of above mentioned substantially rectangular light refraction area, which lens may easily be adapted for giving other types of light refraction, and which lens also can be manufactured very simply.